This invention relates generally to a gas turbine engine, and, more specifically, to diffusion tips of fuel nozzles used within gas turbine engines.
At least some known gas turbine engines ignite a fuel-air mixture in a combustor to generate a combustion gas stream that is channeled downstream to a turbine via a hot gas path. Compressed air is channeled to the combustor from a compressor. Known combustor assemblies use fuel nozzles that facilitate fuel and air delivery to a combustion zone defined in the combustor. The turbine converts thermal energy in the combustion gas stream to mechanical energy that rotates a turbine shaft. The output of the turbine may be used to power a machine, for example, an electric generator or a pump.
At least some known fuel nozzles include a diffusion tip. The diffusion tip forms a pathway for fuel, air or a combination of both, that works in combination with a main premixing circuit of the fuel nozzle. The integrated fuel and/or air mixture is discharged from the tip for ignition, prior to being channeled to a combustion zone.
During operation, fuel and/air is typically channeled through a plurality of passages formed within known diffusion tips and then combusted after exiting the diffusion tip. As a result, an exterior surface of the diffusion tip may be exposed to high temperature combustion gases. Continued exposure to the high temperatures may induce thermal stresses in the diffusion tip. Over time, such thermal stresses may cause cracking and/or mechanical failure of the diffusion tip. To facilitate reducing the temperature of the diffusion tip, at least some known diffusion tips include various cooling circuits. However, such cooling circuits may produce a fuel rich environment which may increase the formation of undesirable soot deposits on the diffusion tip. Soot deposits may adversely affect flow characteristics within the fuel nozzle and/or may increase the combustion temperature. The combination of altered flow characteristics and increased temperatures may adversely affect the operation of fuel nozzle components. For example, thermal degradation or annealing of the metallic alloys may result in reducing the structural integrity of the components.
Moreover, an increase in the operating temperature of a diffusion tip may also cause premature wear of the combustor hardware adjacent to the flame, such as, for example, a combustor liner, and/or transition piece assembly. As a result, such combustor hardware may require replacement more frequently than if the combustion temperatures were maintained at a lower temperature or greater reparability costs. To accommodate the operation with higher temperatures, at least some known combustors use components that are fabricated from special metal alloys that are more resistant to thermal wear. However, such components may add cost and/or weight to the engine as compared to engines having combustors that do not include thermally resistant components made from such alloys.